An organic light emitting device is formed of two opposite electrodes and thin films of organic materials having multilayered semiconductor properties existing therebetween. The organic light emitting device of the above configuration uses a phenomenon where electric energy is converted into light energy by using an organic material, that is, an organic light emission phenomenon. In detail, in the structure where an organic material layer is disposed between an anode and a cathode, if a voltage is applied between two electrodes, holes are injected to the organic material layer in the anode and electrons are injected into the organic material layer in the cathode. When the injected holes and electrons meet each other, an exciton is formed, and the exciton falls down again to a bottom state to emit light.
In the above organic light emitting device, light that is generated in the organic material layer is discharged through a light transmissive electrode, and the organic light emitting device may be generally classified into a top emission type, a bottom emission type and a dual emission type. In the case of the top emission or bottom emission type, one of two electrodes needs to be a light transmissive electrode, and in the case of the dual emission type, both the two electrodes need to be a light transmissive electrode.
In respect to the organic light emitting device, many studies have been concentrated since Kodak, Co. Ltd. announced that in the case where the multilayer structure is used, driving at low voltage is implemented, and recently, a natural color display using the organic light emitting device is attached to a mobile phone and commercialized.
In addition, a study for the recent organic light emitting device using a phosphorescent material instead of a known fluorescent material has been made, such that efficiency has been rapidly improved, and it is expected that the device would be able to replace a known lighting in the near future.
In order to use the organic light emitting device as lighting, unlike a known natural color display, the device should be driven at high brightness, and a constant brightness should be maintained like a known lighting. In order to sufficiently improve brightness of the organic light emitting device, light emission should be implemented in a large area, and in order to implement light emission in the large area, a high driving current should be used. In addition, in order to maintain the constant brightness in the large area, the aforementioned high current needs to be uniformly injected into the device having the large area.
In general, as the anode material of the organic light emitting device, metal oxide having a large work function is mainly used. However, the electroconductivity of the metal oxide is not relatively high. Accordingly, in the case where the metal oxide is used in an organic EL or an LCD having a small display area, there is no problem, but in the case where the metal oxide is used in an organic EL having a large area for being used in lighting devices, a voltage drop by a high current is large, such that the current is not uniformly injected into a light emission surface, and therefore light emission of the device is not uniformly implemented. For example, light is emitted only in the vicinity of a portion in which an electrode is electrically connected to a driving circuit, and weak light emission or no light emission may occur in the other regions.
Meanwhile, as the cathode material of the organic light emitting device, metal having a small work function or an alloy thereof is mainly used. The above metal may have the high electroconductivity of the material, but in the case where transparency of the electrode is required because of characteristics of the organic light emitting device, if the electrode is formed of a thin film, the electroconductivity is decreased. Therefore, even in this case, since current is not uniformly injected onto a light emission surface, light emission of the device may not uniformly occur.
Therefore, in order to use the organic light emitting device as the lighting device, the light emission of high brightness needs to uniformly occur in the device having the large area by decreasing resistance of the electrode.